CN111797490B - Method and equipment for designing safe density of drilling fluid - Google Patents
Method and equipment for designing safe density of drilling fluid Download PDFInfo
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Abstract
The embodiment of the invention provides a method and equipment for designing the safe density of drilling fluid, wherein the method comprises the following steps: establishing a drilling fluid liquid column pressure calculation model for maintaining the stability of the well wall of the target well; acquiring geomechanical parameters of surrounding rocks of the target well; and calculating a model according to the geomechanical parameters of the surrounding rocks and the pressure of the drilling fluid column to obtain the safe density of the drilling fluid of the target well.
Description
Technical Field
The embodiment of the invention relates to the technical field of oil-gas exploration and development, in particular to a method and equipment for designing the safety density of drilling fluid.
Background
In the process of drilling an oil-gas well, in the process of drilling a stratum to form a well hole, the well wall can generate obvious displacement to cause the well wall to crack and collapse, so that reasonable drilling fluid density is set, the occurrence of well wall displacement is inhibited, the well wall can be prevented from cracking or collapsing to the maximum extent, the stability of the well wall is maintained, and the drilling fluid density has a crucial effect on maintaining the stability of the well wall in the drilling process. If the density of the drilling fluid is too low, overflow or blowout can be caused; if the density of the drilling fluid is too high, lost circulation can be caused, so that the drilling fluid invades into the stratum to cause reservoir damage. Designing an optimal drilling fluid density is therefore critical to the exploration and development of oil and gas.
At present, the existing drilling fluid density design method generally calculates the collapse pressure and the fracture pressure of rock by using a rock yield criterion, and then determines the safe density window of the drilling fluid according to the collapse pressure and the fracture pressure. Collapse pressure corresponds to shear failure of the well wall and burst pressure corresponds to tensile failure of the well wall.
However, the inventors have found that the above prior art has at least the following technical problems: because the difference between the collapse pressure and the fracture pressure calculated by different rock yield criteria is large, some designs are conservative, the drilling effect is influenced, and some designs have low safety, so that accidents are easy to happen.
Disclosure of Invention
The embodiment of the invention provides a method and equipment for designing the safety density of drilling fluid, which aim to solve the problems that the difference between collapse pressure and fracture pressure calculated by different rock yield criteria is large, some designs are conservative, the drilling effect is influenced, and some have low safety and are easy to cause accidents.
In a first aspect, an embodiment of the present invention provides a method for designing safe density of drilling fluid, including:
establishing a drilling fluid liquid column pressure calculation model for maintaining the stability of the well wall of the target well;
acquiring geomechanical parameters of surrounding rocks of the target well;
and calculating a model according to the geomechanical parameters of the surrounding rocks and the pressure of the drilling fluid column to obtain the safe drilling fluid density of the target well.
In one possible design, the creating a computational model of the pressure of the drilling fluid column that maintains the stability of the wall of the target well includes:
and according to the stress analysis of the well bore of the target well and the surrounding stratum, establishing a drilling fluid liquid column pressure calculation model for maintaining the stability of the well wall of the target well by adopting an elasticity theory.
In one possible design, the obtaining of the surrounding rock geomechanical parameters of the target well comprises:
and calculating the elastic modulus and the Poisson ratio of the target well stratum according to the acoustic logging information, wherein the acoustic logging information is the acoustic logging information of the target well stratum, calculating the stratum pore pressure of the target well by adopting an Eton method, and calculating the maximum horizontal ground stress and the minimum horizontal ground stress of the stratum of the target well by adopting a combined spring model.
In one possible design, the calculation model of the pressure of the drilling fluid column for maintaining the stability of the wall of the target well is:
in the formula, p w The drilling fluid column pressure is MPa; sigma H Maximum horizontal ground stress, MPa; sigma h Is the minimum horizontal ground stress, MPa; mu is Poisson's ratio of rock around the well, and is dimensionless; theta is a polar angle and is dimensionless.
In one possible design, calculating the elastic modulus and poisson's ratio of the target well formation from the sonic logging data includes:
wherein E is the stratum elastic modulus, MPa; mu is Poisson's ratio and has no dimensional quantity; rho is the stratum density, g/cm 3 ；Δt s The transverse wave time difference of the acoustic logging is μ s/m; Δ t c The longitudinal wave time difference of the acoustic logging is μ s/m.
In one possible design, calculating a formation pore pressure of the target well using the eaton method based on the acoustic log data comprises:
G p ＝G op -(G op -ρ w )(Δt/Δt n ) n
in the formula, G p The pore pressure gradient of the stratum at the well depth H is MPa/m; g op The pressure gradient of the overburden at the well depth H is MPa/m; ρ is a unit of a gradient w The pressure gradient of the formation water at the well depth H is MPa/m; delta t is the measured sound of stratum at the well depth HWave time difference, μ s/m; Δ t n The normal trend value of the acoustic wave time difference of the stratum at the well depth H is μ s/m; n is the Eton index, dimensionless;
according to formation pore pressure gradient G p Calculating formation pore pressure P of target well p ＝G p H, wherein H is the well depth.
In one possible design, calculating a maximum horizontal geostress and a minimum horizontal geostress of the formation of the target well using a combination spring model based on the sonic logging data includes:
in the formula, σ H Maximum horizontal ground stress, MPa; sigma h Is the minimum horizontal ground stress, MPa; e is the rock elastic modulus, MPa; mu is rock Poisson's ratio and is dimensionless; sigma v Overburden pressure, MPa; α is the Biot coefficient; p p Is the formation pore pressure, MPa; epsilon H The structural stress coefficient in the maximum horizontal ground stress direction is dimensionless; epsilon h The structural stress coefficient is the smallest horizontal stress direction and is dimensionless.
In one possible design, the polar angle takes on a value of π/2.
In one possible design, the obtaining a safe drilling fluid density for the target well based on the geomechanical parameters of the surrounding rock and the calculated model of drilling fluid column pressure comprises:
will be the maximum horizontal ground stress σ H Minimum level of ground stress σ h Leading the Poisson ratio mu and the polar angle theta of rocks around the well into the drilling fluid column pressure calculation model to obtain the drilling fluid column pressure at the well depth H;
according to the conversion formula of drilling fluid column pressure and drilling fluid density at the well depth H
And obtaining the density of the drilling fluid at the well depth H.
In a second aspect, an embodiment of the present invention provides an apparatus for designing safe density of drilling fluid, including: at least one processor and memory;
the memory stores computer execution instructions;
the at least one processor executing the computer-executable instructions stored by the memory causes the at least one processor to perform the method of designing a safe drilling fluid density as set forth in the first aspect and the various possible designs of the first aspect above.
According to the method and the device for designing the safe density of the drilling fluid, a drilling fluid column pressure calculation model for maintaining the stability of the well wall of a target well is established; acquiring geomechanical parameters of surrounding rocks of the target well; and calculating a model according to the geomechanical parameters of the surrounding rocks and the pressure of the drilling fluid column to obtain the safe drilling fluid density of the target well, wherein the drilling fluid density designed by the embodiment of the invention is between the pore pressure and the closing pressure of the rocks, and meets the actual requirement of maintaining the stability of the well wall.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic flow diagram of a method for designing safe drilling fluid density according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of forces exerted on surrounding rocks of a target well according to an embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating a comparison between a drilling fluid density and a real drilling density calculated by a drilling fluid safe density design method according to an embodiment of the invention for a well;
FIG. 4 is a schematic structural diagram of an apparatus for designing safe drilling fluid density according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a hardware structure of a device for designing safe drilling fluid density according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Fig. 1 is a schematic flow chart of a method for designing safe drilling fluid density according to an embodiment of the present invention. The execution subject in this embodiment may be a terminal, and may also be a server, and this embodiment is not limited herein specifically, and the method includes:
s101: and establishing a drilling fluid liquid column pressure calculation model for maintaining the stability of the well wall of the target well.
In the embodiment of the invention, the stress analysis of the borehole and the surrounding stratum of the target well can be used for establishing the drilling fluid liquid column pressure calculation model for maintaining the stability of the borehole wall of the target well by adopting an elasticity theory.
Specifically, the calculation model of the pressure of the drilling fluid column for maintaining the stability of the borehole wall of the target well is as follows:
in the formula, p w Is the drilling fluid column pressure, MPa; sigma H Maximum horizontal ground stress, MPa; sigma h Is the minimum horizontal ground stress, MPa; mu is Poisson's ratio of rock around the well, and is dimensionless; theta is a polar angle and is dimensionless.
Referring to FIG. 2, the surrounding rock receiver for the target wellForce diagram. Wherein p is w Is the pressure of the drilling fluid column, σ H To maximum horizontal ground stress, σ h θ is the polar angle for minimum horizontal ground stress. The middle circle represents the borehole wall.
In a polar coordinate system, the angle between the polar axis and the line connecting any point on the plane to the pole is called the polar angle. In one embodiment of the invention, the polar angle takes a value of π/2.
S102: and acquiring geomechanical parameters of surrounding rocks of the target well.
In an embodiment of the present invention, the acquiring geomechanical parameters of surrounding rocks of the target well includes: and calculating the elastic modulus and the Poisson ratio of the stratum of the target well according to the acoustic logging information, wherein the acoustic logging information is the acoustic logging information of the stratum of the target well, calculating the stratum pore pressure of the target well by adopting an Eton method, and calculating the maximum horizontal ground stress and the minimum horizontal ground stress of the stratum of the target well by adopting a combined spring model.
Specifically, according to the acoustic logging information, the elastic modulus and the poisson ratio of the target well stratum are calculated, and the method comprises the following steps:
wherein E is the stratum elastic modulus, MPa; mu is Poisson's ratio and has no dimensional quantity; rho is the stratum density, g/cm 3 ；Δt s The transverse wave time difference of the acoustic logging is [ mu ] s/m; Δ t c The longitudinal wave time difference of the acoustic logging is μ s/m.
According to the acoustic logging information, calculating the formation pore pressure of the target well by adopting an Eton method, wherein the method comprises the following steps:
G p ＝G op -(G op -ρ w )(Δt/Δt n ) n
in the formula, G p The pore pressure gradient of the stratum at the well depth H is MPa/m; g op The pressure gradient of the overburden at the well depth H is MPa/m; rho w The pressure gradient of the formation water at the well depth H is MPa/m; delta t is the actually measured acoustic time difference of the stratum at the well depth H, mu s/m; Δ t n The normal trend value of the acoustic wave time difference of the stratum at the well depth H is μ s/m; n is the Eton index, dimensionless;
according to formation pore pressure gradient G p Calculating formation pore pressure P of target well p ＝G p H, wherein H is the well depth.
Calculating the maximum horizontal ground stress and the minimum horizontal ground stress of the stratum of the target well by adopting a combined spring model according to the acoustic logging information, wherein the method comprises the following steps:
in the formula, σ H Maximum horizontal ground stress, MPa; sigma h Minimum horizontal ground stress, MPa; e is the rock elastic modulus, MPa; mu is rock Poisson ratio and is dimensionless; sigma v Overburden pressure, MPa; α is the Biot coefficient; p p Is the formation pore pressure, MPa; epsilon H The structural stress coefficient in the maximum horizontal ground stress direction is dimensionless; epsilon h The structural stress coefficient is the smallest horizontal stress direction and is dimensionless.
S103: and calculating a model according to the geomechanical parameters of the surrounding rocks and the pressure of the drilling fluid column to obtain the safe drilling fluid density of the target well.
In the present embodiment, the stress σ will be the maximum level H Minimum level of ground stress σ h Leading the Poisson ratio mu and the polar angle theta of rocks around the well into the drilling fluid column pressure calculation model to obtain the drilling fluid column pressure at the well depth H; conversion according to drilling fluid column pressure and drilling fluid density at well depth HFormula (II)
And obtaining the density of the drilling fluid at the well depth H.
From the above description, a drilling fluid column pressure calculation model for maintaining the stability of the well wall of the target well is established; acquiring geomechanical parameters of surrounding rocks of the target well; and calculating a model according to the geomechanical parameters of the surrounding rocks and the pressure of the drilling fluid column to obtain the safe density of the drilling fluid of the target well.
The drilling fluid density calculated by the drilling fluid safety density design method of the embodiment of the invention is compared with the drilling fluid density design threshold value, namely the actual drilling density.
Referring to fig. 3, fig. 3 is a schematic diagram illustrating a comparison between a drilling fluid density calculated by a drilling fluid safety density design method according to an embodiment of the present invention and a drilling fluid density design threshold value, that is, a drilling density in a certain well.
Referring to fig. 3, it can be seen that the drilling fluid density (the "calculated density" in fig. 3) calculated by the drilling fluid safety density design method according to the embodiment of the present invention is between the pore pressure and the closing pressure, and meets the actual requirement of safe drilling; "actual drilling density" is the actual drilling fluid density on site. The "equivalent density of the pressure acting on the well wall" corresponding to the pressure acting on the well wall also takes the pump pressure into account (wherein the equivalent density of the pressure acting on the well wall = the solid drilling density + the density converted by the pump pressure). The drilling fluid density (the 'calculated density' in figure 3) calculated by adopting the drilling fluid safety density design method of the embodiment of the invention is closer to the 'equivalent density' on the actual well wall, thereby meeting the actual requirement.
Fig. 4 is a schematic structural diagram of a device for designing safe drilling fluid density according to an embodiment of the present invention. As shown in fig. 4, the apparatus 40 of the drilling fluid safe density design comprises:
the model building module 401 is used for building a drilling fluid liquid column pressure calculation model for maintaining the stability of the well wall of the target well;
a parameter obtaining module 402, configured to obtain geomechanical parameters of surrounding rocks of the target well;
and a drilling fluid safety density calculation module 403, configured to calculate a model according to the geomechanical parameters of the surrounding rocks and the pressure of the drilling fluid column, so as to obtain the drilling fluid safety density of the target well.
The device provided in this embodiment may be configured to implement the technical solutions of the method embodiments, and the implementation principles and technical effects are similar, which are not described herein again.
In an embodiment of the present invention, the model building module 401 is specifically configured to build, according to the force analysis of the borehole of the target well and the surrounding stratum, the drilling fluid column pressure calculation model for maintaining the borehole wall of the target well stable by using an elastic theory.
In an embodiment of the present invention, the parameter obtaining module 402 is specifically configured to calculate an elastic modulus and a poisson ratio of the target well formation according to acoustic logging data, where the acoustic logging data are acoustic logging data of the target well formation, calculate a formation pore pressure of the target well by using an eaton method, and calculate a maximum horizontal ground stress and a minimum horizontal ground stress of the formation of the target well by using a combined spring model.
In an embodiment of the present invention, the calculation model of the pressure of the drilling fluid column for maintaining the stability of the borehole wall of the target well is:
in the formula, p w The drilling fluid column pressure is MPa; sigma H Maximum horizontal ground stress, MPa; sigma h Is the minimum horizontal ground stress, MPa; mu is Poisson's ratio of rock around the well, and is dimensionless; theta is a polar angle and is dimensionless.
In one embodiment of the present invention, calculating the elastic modulus and poisson's ratio of the target well formation from the sonic logging data comprises:
wherein E is the stratum elastic modulus, MPa; mu is Poisson's ratio and has no dimensional quantity; rho is the stratum density, g/cm 3 ；Δt s The transverse wave time difference of the acoustic logging is [ mu ] s/m; Δ t c The longitudinal wave time difference of the acoustic logging is μ s/m.
In an embodiment of the present invention, the parameter obtaining module 402 is specifically configured to calculate a formation pore pressure of the target well by using an eaton method according to the acoustic logging data, and includes:
G p ＝G op -(G op -ρ w )(Δt/Δt n ) n
in the formula, G p The pressure gradient of stratum pores at the well depth H is MPa/m; g op The pressure gradient of the overburden at the well depth H is MPa/m; rho w The pressure gradient of the formation water at the well depth H is MPa/m; delta t is the actually measured acoustic time difference of the stratum at the well depth H, mu s/m; Δ t n The normal trend value of the acoustic wave time difference of the stratum at the well depth H is μ s/m; n is the Eton index, dimensionless;
according to formation pore pressure gradient G p Calculating formation pore pressure P of target well p ＝G p H, wherein H is the well depth.
In an embodiment of the present invention, the parameter obtaining module 402 is specifically configured to calculate a maximum horizontal ground stress and a minimum horizontal ground stress of a formation of the target well by using a combined spring model according to the sonic logging data, and includes:
in the formula, σ H Maximum horizontal ground stress, MPa; sigma h Is the minimum horizontal ground stress, MPa; e is the elastic modulus of rock, MPa; mu is rock Poisson's ratio and is dimensionless; sigma v Overburden pressure, MPa; α is the Biot coefficient; p is p Is the formation pore pressure, MPa; epsilon H The structural stress coefficient in the direction of the maximum horizontal ground stress is dimensionless; epsilon h The constructional stress coefficient for the direction of the minimum horizontal ground stress is dimensionless.
In one embodiment of the invention, the drilling fluid safety density calculation module 403 is specifically adapted to calculate the maximum horizontal stress σ H Minimum level of ground stress σ h Leading the Poisson ratio mu and the polar angle theta of the rock around the well into the drilling fluid column pressure calculation model to obtain the drilling fluid column pressure at the well depth H;
converting formula according to drilling fluid column pressure and drilling fluid density at well depth H
And obtaining the density of the drilling fluid at the well depth H.
The device provided in this embodiment may be configured to implement the technical solutions of the method embodiments, and the implementation principles and technical effects are similar, which are not described herein again.
Fig. 5 is a schematic diagram of a hardware structure of a device for designing safe drilling fluid density according to an embodiment of the present invention. As shown in fig. 5, the apparatus 50 of the drilling fluid safe density design of the present embodiment includes: a processor 501 and a memory 502; wherein
A memory 502 for storing computer-executable instructions;
the processor 501 is configured to execute the computer-executable instructions stored in the memory to implement the steps performed by the terminal or the server in the above embodiments. Reference may be made in particular to the description relating to the method embodiments described above.
Alternatively, the memory 502 may be separate or integrated with the processor 501.
When the memory 502 is provided independently, the drilling fluid safe density design apparatus further includes a bus 503 for connecting the memory 502 and the processor 501.
Embodiments of the present invention further provide a computer-readable storage medium, in which computer-executable instructions are stored, and when a processor executes the computer-executable instructions, the method for designing safe drilling fluid density as described above is implemented.
In the embodiments provided in the present invention, it should be understood that the disclosed apparatus and method may be implemented in other ways. For example, the above-described device embodiments are merely illustrative, and for example, the division of the modules is only one logical division, and other divisions may be realized in practice, for example, a plurality of modules may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or modules, and may be in an electrical, mechanical or other form.
The modules described as separate parts may or may not be physically separate, and parts displayed as modules may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment.
In addition, functional modules in the embodiments of the present invention may be integrated into one processing unit, or each module may exist alone physically, or two or more modules are integrated into one unit. The unit formed by the modules can be realized in a hardware form, and can also be realized in a form of hardware and a software functional unit.
The integrated module implemented in the form of a software functional module may be stored in a computer-readable storage medium. The software functional module is stored in a storage medium and includes several instructions for enabling a computer device (which may be a personal computer, a server, or a network device) or a processor (processor) to execute some steps of the methods according to the embodiments of the present application.
It should be understood that the Processor may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), etc. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like. The steps of a method disclosed in connection with the present invention may be embodied directly in a hardware processor, or in a combination of hardware and software modules.
The memory may comprise a high-speed RAM memory, and may further comprise a non-volatile storage NVM, such as at least one disk memory, and may also be a usb disk, a removable hard disk, a read-only memory, a magnetic or optical disk, etc.
The bus may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, an Extended ISA (EISA) bus, or the like. The bus may be divided into an address bus, a data bus, a control bus, etc. For ease of illustration, the buses in the figures of the present application are not limited to only one bus or one type of bus.
The storage medium may be implemented by any type or combination of volatile or non-volatile memory devices, such as Static Random Access Memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic or optical disks. A storage media may be any available media that can be accessed by a general purpose or special purpose computer.
An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. Of course, the storage medium may also be integral to the processor. The processor and the storage medium may reside in an Application Specific Integrated Circuits (ASIC). Of course, the processor and the storage medium may reside as discrete components in an electronic device or host device.
Those of ordinary skill in the art will understand that: all or a portion of the steps of implementing the above-described method embodiments may be performed by hardware associated with program instructions. The program may be stored in a computer-readable storage medium. When executed, the program performs steps comprising the method embodiments described above; and the aforementioned storage medium includes: various media that can store program codes, such as ROM, RAM, magnetic or optical disks.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.
Claims (5)
1. A method of drilling fluid safe density design, comprising:
establishing a drilling fluid liquid column pressure calculation model for maintaining the stability of the well wall of the target well;
acquiring geomechanical parameters of surrounding rocks of the target well;
calculating a model according to the geomechanical parameters of the surrounding rocks and the pressure of the drilling fluid column to obtain the safe drilling fluid density of the target well;
the drilling fluid liquid column pressure calculation model for maintaining the stability of the well wall of the target well is as follows:
in the formula, p w The drilling fluid column pressure is MPa; sigma H Maximum horizontal ground stress, MPa; sigma h Minimum horizontal ground stress, MPa; mu is Poisson's ratio of rock around the well, and is dimensionless; theta is a polar angle and is dimensionless;
the obtaining of the geomechanical parameters of surrounding rocks of the target well comprises:
according to acoustic logging information, calculating the elastic modulus and the Poisson ratio of the stratum of the target well, wherein the acoustic logging information is the acoustic logging information of the stratum of the target well, calculating the stratum pore pressure of the target well by adopting an Eton method, and calculating the maximum horizontal ground stress and the minimum horizontal ground stress of the stratum of the target well by adopting a combined spring model;
calculating the elastic modulus and Poisson's ratio of the target well stratum according to the acoustic logging information, and the method comprises the following steps:
wherein E is the stratum elastic modulus, MPa; mu is Poisson's ratio and has no dimensional quantity; rho is the stratum density, g/cm 3 ；Δt s The transverse wave time difference of the acoustic logging is [ mu ] s/m; Δ t c The longitudinal wave time difference of the acoustic logging is μ s/m;
calculating the formation pore pressure of the target well by adopting an Eton method according to the acoustic logging information, and the method comprises the following steps:
G p ＝G op -(G op -ρ w )(Δt/Δt n ) n
in the formula, G p Is a wellThe pressure gradient of stratum pores at the deep H position is MPa/m; g op The pressure gradient of the overburden at the well depth H is MPa/m; ρ is a unit of a gradient w Is the formation water pressure gradient at the well depth H, MPa/m; delta t is the actually measured acoustic time difference of the stratum at the well depth H, mu s/m; Δ t n The normal trend value of the acoustic wave time difference of the stratum at the well depth H is μ s/m; n is the Eton index, dimensionless;
according to formation pore pressure gradient G p Calculating formation pore pressure P of target well p ＝G p H, wherein H is the well depth;
calculating the maximum horizontal ground stress and the minimum horizontal ground stress of the stratum of the target well by adopting a combined spring model according to the acoustic logging information, wherein the method comprises the following steps:
in the formula, σ H Maximum horizontal ground stress, MPa; sigma h Minimum horizontal ground stress, MPa; e is the elastic modulus of rock, MPa; mu is rock Poisson ratio and is dimensionless; sigma v Overburden pressure, MPa; α is the Biot coefficient; p is p Is the formation pore pressure, MPa; epsilon H The structural stress coefficient in the maximum horizontal ground stress direction is dimensionless; epsilon h The structural stress coefficient is the smallest horizontal stress direction and is dimensionless.
2. The method of claim 1, wherein the establishing a computational model of drilling fluid column pressure that maintains the stability of the walls of the target well comprises:
and according to the stress analysis of the borehole of the target well and the surrounding stratum, establishing a drilling fluid liquid column pressure calculation model for maintaining the stability of the borehole wall of the target well by adopting an elasticity theory.
3. The method of claim 1, wherein the polar angle is at a value of pi/2.
4. The method of claim 1 or 3, wherein said deriving a drilling fluid safe density for the target well from the surrounding rock geomechanical parameters and the drilling fluid column pressure calculation model comprises:
will be the maximum horizontal ground stress σ H Minimum level of ground stress σ h Leading the Poisson ratio mu and the polar angle theta of rocks around the well into the drilling fluid column pressure calculation model to obtain the drilling fluid column pressure at the well depth H;
according to the conversion formula of drilling fluid column pressure and drilling fluid density at the well depth H
And obtaining the density of the drilling fluid at the well depth H.
5. An apparatus for designing safe density of drilling fluid, comprising: at least one processor and memory;
the memory stores computer-executable instructions;
the at least one processor executing the computer-executable instructions stored by the memory cause the at least one processor to perform the method of drilling fluid safety density design of any of claims 1-4.
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